build: fix fortran flags on mac

m4/ax_mexopts.m4

@@ -66,17 +66,15 @@ case ${MATLAB_ARCH} in
     MACOSX_DEPLOYMENT_TARGET='10.6'
     if test "${MATLAB_ARCH}" = "maci"; then
         ARCHS='i386'
-        MATLAB_FFLAGS=''
     else
         ARCHS='x86_64'
-        MATLAB_FFLAGS='-m64'
     fi
     MATLAB_DEFS="$MATLAB_DEFS -DNDEBUG"
     MATLAB_CFLAGS="-fno-common -no-cpp-precomp -arch $ARCHS -isysroot $SDKROOT -mmacosx-version-min=$MACOSX_DEPLOYMENT_TARGET -fexceptions -O2"
     MATLAB_LDFLAGS="-L$MATLAB/bin/${MATLAB_ARCH} -Wl,-twolevel_namespace -undefined error -arch $ARCHS -Wl,-syslibroot,$SDKROOT -mmacosx-version-min=$MACOSX_DEPLOYMENT_TARGET -bundle -Wl,-exported_symbols_list,\$(top_srcdir)/mexFunction-MacOSX.map"
     MATLAB_LIBS="-lmx -lmex -lmat -lstdc++ -lmwlapack"
     MATLAB_CXXFLAGS="-fno-common -no-cpp-precomp -fexceptions -arch $ARCHS -isysroot $SDKROOT -mmacosx-version-min=$MACOSX_DEPLOYMENT_TARGET -O2"
-    MATLAB_FFLAGS="-fexceptions $MATLAB_FFLAGS -fbackslash"
+    MATLAB_FFLAGS="-fexceptions -fbackslash -arch $ARCHS"
     # Starting from MATLAB 7.5, BLAS and LAPACK are in distinct libraries
     AX_COMPARE_VERSION([$MATLAB_VERSION], [ge], [7.5], [MATLAB_LIBS="${MATLAB_LIBS} -lmwblas"])
     ax_mexopts_ok="yes"